Gas turbine power plants for generating electricity are well known in the art and typically utilize a gas turbine engine, a fuel system, a power turbine, a generator and an engine control. Conventional gas turbine engines of the type typically used in gas turbine power plants include a low pressure rotor comprised of a low pressure compressor directly connected by a first shaft to a downstream low pressure turbine. In addition, the gas turbine engine has a high pressure rotor disposed between the low pressure compressor and the low pressure turbine. The high pressure rotor is comprised of a high pressure compressor directly connected by a second shaft to a downstream high pressure turbine. Further, the gas turbine engine includes a burner, which is disposed between the high pressure compressor and the high pressure turbine. The burner receives compressed air and a fuel flow from the fuel system.
The fuel system includes a first fuel supply line between the fuel supply and a fuel valve, and a second fuel supply line from the fuel valve to the burner. The fuel flow is modulated by the fuel valve or control/shutoff/trip/flow valve, which is driven by an actuator. An injection device introduces water or steam along with the fuel into the burner. The fuel used may be liquid fuel, gaseous fuel or a combination of the two.
The gas turbine power plants further have the power turbine located downstream of the gas turbine engine. The power turbine has a power turbine shaft adapted to fixedly engage a generator shaft. The generator shaft is connected to the generator. Typically, the power plants also include the engine control for measuring various parameters during operation and for adjusting performance of the system. Oftentimes, conventional power plants will also include a boiler for producing steam from water.
In operation, inlet air flows through the low and high compressors, thereby producing compressed air which flows to the burner. When the fuel valve is in the open position, fuel flows to the burner. In order to achieve increased power output and decrease emissions, in accordance with well-known gas turbine principles, the injection device introduces water or steam along with the fuel into the burner in response to the exit gas temperature between the low pressure compressor and the power turbine. The burner provides ignition of the fuel/air mixture causing a jet exhaust to be created. The jet exhaust flows downstream and passes through the two turbines driving the first and second shafts, which in turn causes the two compressors upstream to rotate. The rotation of the compressors supplies the burner with the necessary inlet air.
After the jet exhaust passes through the two turbines, the jet exhaust flows through the power turbine driving it, thereby producing mechanical energy. The mechanical energy is in the form of the rotation of the turbine shaft and the coupled generator shaft. The generator converts this mechanical energy into electrical energy. If the power plant has a boiler, the effluent from the power turbine is flowed to the boiler in a heat transfer relationship with water, consequently steam is produced.
One problem with gas turbine power plants is burner blowout which occurs when the burner fails to ignite the fuel/air mixture. As a result, unburned fuel enters the power plant downstream of the burner. Burner blowout occurs due to changes in the fuel/air ratio of the fuel/air mixture fed to the burner.
Firstly, the fuel/air ratio is dictated by the gas turbine engine design and varies somewhat through the load range and during transient phenomenon occurring in the power plant prior to reaching a steady-state condition. In the event that the fuel/air ratio decreases significantly, the mixture of fuel and air fed to the burner can be so lean that the burner is not supplied with enough fuel to maintain the ignition and a blowout occurs. In contrast, if the fuel/air ratio increases significantly, the mixture of fuel and air fed to the burner can be lacking sufficient air so that the burner cannot maintain the ignition and a blowout occurs.
Secondly, while the injection of water or steam has some positive impact on the power plant, the injection into the fuel changes the burner's sensitivity to the fuel/air ratio making the burner more unstable and more susceptible to blowout.
The most serious consequence of burner blowout may occur in power plants that have boilers which use the effluent from the power turbine. In these types of power plants, the introduction of unburned fuel into the boiler can lead to an explosion. This explosion occurs when the unburned fuel auto-ignites due to contact with the hot turbine parts and this ignited fuel causes unburned fuel which has accumulated in the boiler to ignite. Explosions have been observed to generally occur if blowout persists from about 0.00 seconds to about 0.4 seconds.
Thus, a method and apparatus are necessary for detecting burner blowout so that fuel flow to the burner can be stopped, thereby avoiding the consequences of introducing unburned fuel into the power plant. A method and apparatus designed to detect burner blowout is described in commonly-owned U.S. Pat. No. 5,235,802 and commonly-owned U.S. Pat. No. 5,170, 621, respectively. The method and apparatus disclosed in the aforementioned patents, address blowout detection by continuously monitoring a fuel demand signal and measuring a low pressure rotor speed, which is indicative of the actual airflow. A flame failure exists and fuel flow to the burner is stopped, if the fuel/air ratio exceeds certain pre-selected values. The pre-selected values vary depending on whether the operation is below or above idle.
Although the method and apparatus disclosed in U.S. Pat. Nos. 5,235,802 and 5,170,621 detect flame failure, these solutions may require too long a response time to minimize the consequences of burner blowout in all cases. As a result, scientists and engineers have been searching for a method and apparatus which will detect blowout with a shorter response time.